ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

CENRAP Modeling: Need for 

36 km versus 12 km Grid 

Resolution

Ralph Morris, Gerard Mansell, Bonyoung Koo and 

Abby Hoats, ENVIRON International Corporation

Gail Tonnesen, Mohammed Omary, Chao-Jung Chien 

and Yingqun Wang UC Riverside

CENRAP Modeling Work Group Meeting

Baton Rouge, Louisiana

February 7, 2006
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Background

• 2002 annual runs using CMAQ and/or CAMx are 

quite resource intensive

– CMAQ 36 km grid 5 days on 36 CPUs & 1,000 Gb output

– CAMx 36 km grid 9 days on 8 CPUs & 200 Gb output

– CMAQ 12 km grid ~2 weeks on 36 CPU & 2,000 Gb

– CAMx 12km grid ~3 weeks on 8 CPUs & 500 Gb output

• SMOKE emissions modeling of 12 km grid also adds 

another 1-3 weeks of processing and 4 Tb of disk 

storage needed

• Preliminary Model Performance Evaluation (MPE) 

did not indicate improvements in model performance 

using 12 km grid
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Purpose

• To determine whether 12 km grid improves 

the CENRAP regional haze modeling 

sufficiently well to justify added 

expense/time

– If 12 km grid does seem justified, can just 12 

km meteorological be used and interpolate 36 

km emissions to achieve the benefits of the 12 

km grid – flexi-nested emissions (FE)
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Approach

• Model three 2002 episodes at 36 km and 12 

km resolution

– Spring: March 7th to April 23th

– Summer: August 27th to September 13th

– Winter: November 26th to December 15th

• CMAQ and CAMx 36km vs. 12km model 

performance comparisons

– Also perform CAMx 12km runs with emissions 

flexi-nested (FE) from 36km emissions
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Spring Episode: CMAQ Modeling

36 km versus 12 km Model Performance

Sulfate (SO4) Nitrate (NO3)
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Spring Episode: CMAQ Modeling

36 km versus 12 km Model Performance

Organic Matter Carbon (OMC) Elemental Carbon (EC)
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Spring Episode: CMAQ Modeling

36 km versus 12 km Model Performance

Soil (Other PM2.5) Coarse Mass (CM)
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Summer Episode: SO4 Performance

CENRAP IMPROVE Monitoring Sites

CMAQ 36km vs. 12km CAMx 36km vs. 12km
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Summer Episode: SO4 Performance

CENRAP CASTNet Monitoring Sites

CMAQ 36km vs. 12km CAMx 36km vs. 12km
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Summer Episode: NO3 Performance

CENRAP IMPROVE Monitoring Sites

CMAQ 36km vs. 12km CAMx 36km vs. 12km
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Summer Episode: OMC Performance

CENRAP IMPROVE Monitoring Sites

CMAQ 36km vs. 12km CAMx 36km vs. 12km
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Summer Episode: EC Performance

CENRAP IMPROVE Monitoring Sites

CMAQ 36km vs. 12km CAMx 36km vs. 12km
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Winter Episode: SO4 Performance

CENRAP IMPROVE Monitoring Sites

CMAQ 36km vs. 12km CAMx 36km vs. 12km
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Winter Episode: NO3 Performance

CENRAP IMPROVE Monitoring Sites

CMAQ 36km vs. 12km CAMx 36km vs. 12km
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Winter Episode: OMC Performance

CENRAP IMPROVE Monitoring Sites

CMAQ 36km vs. 12km CAMx 36km vs. 12km
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Winter Episode: EC Performance

CENRAP IMPROVE Monitoring Sites

CMAQ 36km vs. 12km CAMx 36km vs. 12km
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Conclusions: 36km vs. 12 km

• CMAQ model performance fairly insensitive to use 

of 36km or 12km grid resolution

• CAMx exhibits more sensitivity to 12km grid

– Summer SO4 underprediction bias greatly reduced using 

12 km grid

• Different treatment of clouds?

• Different horizontal diffusion sensitivity?

– CMAQ inversely, whereas CAMx proportional to grid cell size

• High resolution emissions?

• Other?

– What is chief driver in 36km/12km differences?

• Meteorology; Emissions; Model Formulation; Other?

• Use CAMx flexi-nest feature applied to emissions to interpolate 

36km emissions to 12 km; all other inputs at 12km
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

SO4 Effects of 12km versus Flexi-Nest

Emissions at CENRAP IMPROVE Sites 

Summer Winter
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

NO3 Effects of 12km versus Flexi-Nest

Emissions at CENRAP IMPROVE Sites 

Summer Winter
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

OMC Effects of 12km versus Flexi-Nest

Emissions at CENRAP IMPROVE Sites 

Summer Winter
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

EC Effects of 12km versus Flexi-Nest

Emissions at CENRAP IMPROVE Sites 

Summer Winter
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

SO4

-40

-30

-20

-10

0

10

20

30

40

Spring Summer Winter

Fractional Bias (%)

36k 12k

-40

-30

-20

-10

0

10

20

30

40

50

Summer Winter

Fractional Bias (%)

36k 12k 12kFE

SO4 Fractional Bias

36km, 12km, 12kmFE

CMAQ – little 

sensitivity to 12km grid

 CAMx – in 

summer 12km grid 

eliminates bias! 

Flexi-nested 

emissions similar 

to 12km
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

NO3 Fractional Bias

36km, 12km, 12kmFE

CMAQ – some 

sensitivity to 12km grid

 CAMx – little 

sensitivity to 12 km 

grid; flexi-nested 

emissions match 

12 km emission 

performance

NO3

-120

-100

-80

-60

-40

-20

0

20

40

60

80

Spring Summer Winter

Fractional Bias (%)

36k 12k

-150

-100

-50

0

50

100

Summer Winter

Fractional Bias (%)

36k 12k 12kFE
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

OC

0

5

10

15

20

25

30

35

40

Spring Summer Winter

Fractional Bias (%)

36k 12k

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

Summer Winter

Fractional Bias (%)

36k 12k 12kFE

OMC Fractional Bias

36km, 12km, 12kmFE

CMAQ – some 

sensitivity to 12km grid 

– performance changes 

mixed. Winter 

performance worse than 

CAMx

 CAMx – little 

sensitivity to 12 km grid; 

flexi-nested emissions 

match 12 km emission 

performance
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

EC

-60

-50

-40

-30

-20

-10

0

10

20

Spring Summer Winter

Fractional Bias (%)

36k 12k

-50

-40

-30

-20

-10

0

10

20

30

40

Summer Winter

Fractional Bias (%)

36k 12k 12kFE

EC Fractional Bias

36km, 12km, 12kmFE

CMAQ – small 

sensitivity to 12km grid –

performance changes 

mixed. Winter 

performance improved

 CAMx – small 

sensitivity to 12 km 

grid; flexi-nested 

emissions match 

12 km emission 

performance
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Conclusions: 12km Emissions Need

• Using all 12 km inputs versus all 12 km inputs 

except emissions that are flexi-nested from the 36 

km emissions produces essentially identical 

CAMx model performance in the CENRAP 

domain

– Improved CAMx summer SO4 performance using 12 

km grid appears due to meteorology and model 

formulation, not emissions

– Supports notion that if 12 km modeling is needed may 

be able to flexi-nest emissions

• Significant savings in time and resources
ENVIRON/UCR CENRAP Modeling Workgroup February 6-8, 2006

Recommendations: 12 km Grid

• With the possible exception of CAMx SO4 performance, little 

benefit in model performance seen with use of 12 km grid

• For Regional Haze Modeling at Class I Areas, use of 12 km 

meteorology and 36 km emissions (flexi-nest) probably 

adequate

– If using CAMx can flexi-nest automatically

– If using CMAQ will need an external flexi-nest type program

– Would require processing of 12 km meteorological data

• If analyzing 8-hour ozone and/or PM2.5 may come to different 

recommendation

• Still have not evaluated effects of grid resolution on response to 

emission reductions

– VISTAS found similar 2018 visibility projections using 36km and 12km 

grids